In general, an oriented electrical steel sheet contains approximately 3.1% of Si component in a steel sheet, and refers to an electrical steel sheet having extremely excellent magnetic characteristics in a rolling direction because the orientation of crystal grains has a texture arranged in a {100}<001> direction.
The {100}<001> texture can be obtained by a combination of various processes, and particularly, a series of processes of subjecting components including the components of a steel slab to heating, hot rolling, hot band annealing, primary recrystallization annealing, and final annealing need to be very strictly controlled.
Specifically, since the oriented electrical steel sheet suppresses the growth of primary recrystallized grains and exhibits excellent magnetic characteristics by means of a secondary recrystallized structure obtained by selectively growing crystal grains in a {100}<001> orientation among the crystal grains whose the growth is suppressed, a primary recrystallized grain growth suppressing agent is more important. Moreover, in the final annealing process, it is one of the important matters in a technology of manufacturing an oriented electrical steel sheet to enable crystal grains, which stably have a texture in a {100}<001> orientation among crystal grains whose growth is suppressed to be preferentially grown.
Examples of a primary recrystallized grain growth suppressing agent which may satisfy the aforementioned conditions and is currently and industrially widely used, include MnS, AlN, MnSe, and the like. Specifically, MnS, AlN, MnSe, and the like contained in a steel slab are subjected to a solid solution treatment by being reheated at high temperature for a long period of time, and then hot-rolled, and the components having an appropriate size and distribution in a subsequent cooling process are produced as a precipitate, and thus, may be used as the growth suppressing agent. However, there is a problem in that the steel slab needs to be heated at high temperature.
In this regard, recently, there has been an effort to improve magnetic characteristics of an oriented electrical steel sheet by a method for heating a steel slab at low temperature. For this purpose, a method for adding an antimony (Sb) element to the oriented electrical steel sheet has been proposed, but there has been pointed out a problem in that noise quality of a transformer deteriorates because the crystal grain sizes are irregular and coarse after the final high temperature annealing.
Meanwhile, in order to minimize the power loss of the oriented electrical steel sheet, an insulation coating is generally formed on the surface of the oriented electrical steel sheet, and in this case, the insulation coating basically needs to have high electrical insulating properties, excellent adhesion with materials, and a uniform color having no defects in the appearance. Along with the requirements, due to the recent strengthening of the international regulation on noise of a transformer and the fierce competition among the related industries, there is a need for studies on a magnetic deformation (magnetostriction) phenomenon in order to reduce the noise from an insulation coating of an oriented electrical steel sheet.
Specifically, when an electric field is applied to an electrical steel sheet used as a transformer core, a flicker phenomenon is caused by the repeated shrinkage and expansion, and vibration and noise are caused in a transformer due to the flicker.
In the case of a generally known oriented electrical steel sheet, effects of alleviating the iron loss and reducing the noise resulting from the magnetic deformation have been attempted by forming an insulation coating on a steel sheet and a forsterite-based base coating, and imparting the tensile stress to the steel sheet by using the difference in thermal expansion coefficients of the insulation coatings, but there is a limitation in satisfying a noise level recently required for a high oriented electrical steel sheet.
Meanwhile, as a method for reducing the 90° magnetic domain of an oriented electrical steel sheet, a wet coating method is known. Here, the 90° magnetic domain refers to a region having a magnetization oriented at a right angle with respect to a magnetic field application direction, and as the amount of 90° magnetic domain is decreased, the magnetic deformation is reduced. However, the general wet coating method has a problem in that a space factor and efficiency of a transformer deteriorate due to the disadvantages in that the effect of alleviating the noise by applying the tensile stress is insufficient, and a coating thickness needs to be thick.
In addition, as a method for imparting high tension characteristics to a surface of an oriented electrical steel sheet, a coating method through vacuum deposition such as a physical vapor deposition (PVD) method and a chemical vapor deposition (CVD) method has been known. However, the coating method has a problem in that it is difficult to apply the coating method to a commercial production, and an oriented electrical steel sheet manufactured by the method has degraded insulation characteristics.